Prof. Dr. Dr. h.c. mult. Walter Greiner 1935-2016

The international nuclear physics community mourns the loss of one of our most illustrious, distinguished colleagues,‎ Walter Greiner, internationally renowned scholar, creative scientific pioneer, and good friend.

Walter Greiner, Professor for Theoretical Physics at Goethe University Frankfurt am Main and Senior Fellow at the Frankfurt Institute for Advanced Studies, FIAS, is renowned world-wide for his pioneering role in establishing heavy-ion physics as an independent, rapidly growing research field, and as one of the founding father of GSI, the Helmholtz National Laboratory for Heavy-Ion Research, and the multidisciplinary Frankfurt Institute for Advanced Studies, FIAS.

Walter was born in Thuringia. After the Second World War, when he was a young boy, his family moved to Frankfurt am Main, where he was educated at a chemical plant as a mechanic. He started studying physics at Goethe University in 1956, where he received his BSc in 1959, then moved on to the Technische Hochschule Darmstadt, for his diploma work (MSc) on Plasma reactors in 1960.

Walter earned his Dr. rer. nat. (PhD) with his dissertation on nuclear polarizability in muonic atoms, under the guidance of his mentor, Hans Marschall, at the University of Freiburg in 1961.

When at Freiburg, Walter began to develop, with his friend Amand Faessler, the famous rotation-vibration collective model of nuclear excitations.

A young‎ postdoc, at the age of 27, he moved on to the US. From 1962 to 1964 he was assistant professor at the University of Maryland, were he met his lifelong friend and colleague Judah Moshe Eisenberg. The two ambitious young scientists started to work on their seminal three-volume monograph "Theoretical Nuclear Physics", a textbook-must for generations of graduate students of nuclear physics.

In 1964 Walter accepted an offer to return to Frankfurt as the Chair and Director of the Institute for Theoretical Physics at Goethe University. He ‎was Dean of the faculty in 2001/02, and became founding director of FIAS in 2003, where he remained active as senior fellow until the age 80.

In 1966, Walter Greiner started an initiative for a national heavy-ion laboratory and invited his colleagues at the Hessian Universities for participation. Finally a proposal was submitted to the Federal Ministry of Research and the State of Hesse which was approved in 1969. The new laboratory including the heavy ion accelerator UNILAC was built from 1970 to 1975 and evolved into today‘s world-leading laboratory for heavy-ion research, the GSI. The theoretical basis for this new field of research had been already established by his Frankfurt School of Theoretical Physics.  Many papers on specific problems of heavy ion physics were already published, such as the generation and stability of super-heavy nuclei, cluster channels in nuclear reactions,  nuclear molecules, vacuum polarization and positron emission in overcritical fields. Beyond, he organized first scientific activities at the new laboratory, regular seminars and specific workshops, and took care of the theory division in this rapidly expanding laboratory. 

‎Walter Greiner swiftly acquired a reputation of an excellent, energetic, and visionary scholar - his lecture notes on Theoretical Physics are published in a series of more than 15 textbooks and have been translated into numerous languages. They have taught generations of physics students the foundations of Theoretical Physics, and they are highly appreciated as a reference source due to the richness of their content.

Walter is the founding father of the Frankfurt School of Theoretical Physics at Goethe University. This school attracted students from all over the world to pursue world-leading research in nuclear and heavy-ion physics. More than 150 of his students earned their PhD under Walter's supervision, more than 40 of his students became leading scholars and researchers of theoretical physics and heavy-ion science, world-wide.

Walter's interest in science was phenomenal and not limited to a particular field. His creativity was astounding, he published more than 1000 articles, in a broad variety of fields. In the field of nuclear structure and reactions he developed the ‎aforementioned rotation-vibration collective model, he predicted different proton and neutron deformations in nuclei, he created the Dynamic Collective Model of giant resonances and analyzed the spreading width of giant resonances, he ‎devised the eigenchannel theory of nuclear reactions, he generalized the Collective Model (known as "Gneuß-Greiner” model or also the Frankfurt Collective Model), and he predicted the existence, structure, and properties of superheavy nuclei and their decays, which by now have been identified experimentally up to nuclear charges Z=118.

He and his students developed the Two-Center Shell Model and the theory of nuclear molecules, as well as a new form of  "cluster" radioactivity, which can also be understood as a super-asymmetric nuclear fission. Coulomb-barrier heavy-ion physics and quantum electrodynamics, in particular of strong overcritical fields, the “decay of the vacuum", the theory of supercritical electronic quasimolecules in heavy-ion collisions, and atomic physics were a few of his many passions in physics, further developed in his school.

Walter Greiner pioneered the field of relativistic heavy-ion physics with a seminal prediction that nuclear matter could be heated and compressed in collisions of heavy atomic nuclei via the creation of shock waves. While initially heavily disputed, this prediction was later experimentally confirmed by the observation of strong collective flow in heavy-ion collisions. Heavy-ion collisions are nowadays the primary tool to study compressed and heated strongly interacting matter under controlled laboratory conditions, and give access to its equation of state‎ and phase transitions in such matter. The early Universe has passed through such transitions shortly after the Big Bang, and they may play a prominent role in neutron stars and their mergers into black holes.

Walter predicted a mechanism for the production of clusters of antimatter and strange matter from the highly correlated vacuum (meson field theory) as well as the extension of the periodic system into new directions of strangeness and antimatter in astrophysics and in relativistic heavy-ion collisions.

In astrophysics, with Peter Hess he modified Einsteins ART into “ pseudo-complex general relativity", which avoids the singularities in Schwarzschildt's solutions. Signatures for this pseudo-complex ‎general relativity are bright, narrow ringsegments in front of black holes, presently being searched for actively at large telescopes at international observatories.

Biophysics of the magnetic sense of animals and man, proton and ion tumor therapy, channeling, and X-ray lasers - with a Hirsch index above 100, Walter Greiner has been quoted more than 40 000 times‎, one of the top-quoted scientists world-wide.

Walter’s scientific achievements have earned him eleven honorary doctorates, from renowned universities all over the world. He won the Max-Born prize of the German Physical Society, the Otto-Hahn prize of the City of Frankfurt am Main, the Alexander von Humboldt medal, and he is Officier dans l'Ordre Palmes Académiques.

Walter was not only driven by a life-long passion for physics, he was also deeply concerned with the impact of science on society. He realized that scientific collaborations can serve as a means to reconcile adversaries. Thus, with Judah Eisenberg, he initiated a fruitful scientific exchange in the form of a DFG-funded collaboration between the universities Tel Aviv, Bethlehem, and Frankfurt.

Walter was also acutely aware of the fact that fundamental science must reach society, in order to receive acceptance and be further promoted.

Together with Frankfurt citizens, he founded the ``Förderverein für Physikalische Grundlagenforschung’’ at Goethe University. Here, very much in the tradition of Goethe University as a university founded by the citizens of Frankfurt am Main, sponsors generously donate funds which are used to award students and members of the department of physics for their achievements in research and teaching.

We take a moment to reflect and celebrate a life well lived and the many lives Walter touched.

We remember Walter as one of our field’s most talented and passionate members. He had great breadth and depth in physics.

Besides many solid and accessible works, he published also very visionary contributions of great impact.

Walter was a tireless leader, deeply concerned about the health of the discipline and its impact on society. He was also a father for his students, and a warm friend for his colleagues, who were many and from many regions, representing his passion for the global nature of science. We are sure his legacy of contributions to our field and the world-wide collaborative interactions he helped form will continue. Let us share with you our deepest and sincere condolences to his family and friends.

Rudolf Bock, Dirk Rischke, Horst Stöcker

---